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Two Senate office buildings were briefly evacuated Wednesday because of the smell of smoke. They were reopened minutes later, deemed "safe for re-entry," according to an announcement over the Capitol's public address system.

The cause was a small electrical fire in an air intake unit, according to NBC's Chip Reid.

Fire officials had been called to the Dirksen and Hart buildings, according to a law enforcement official. The fire started in the Dirksen Building, NBC reported.

At one point, Capitol officials were investigating whether the smoke was coming from the roof of the Dirksen building, ah official told NBC.